Can you tell if someone has a mental illness?

Can you tell if someone has a mental illness? Excessive fears or worries, or extreme feelings of guilt. Extreme mood changes of highs and lows. Withdrawal from friends and activities. Significant tiredness, low energy or problems sleeping.

Excessive fears or worries, or extreme feelings of guilt. Extreme mood changes of highs and lows. Withdrawal from friends and activities. Significant tiredness, low energy or problems sleeping.
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